1. Field of the Invention
The present invention relates to reaming frustoconical undercuts in cylindrical holes for placement of expansible bolts therein. More particularly, the invention relates to an improved, expansible rotary power tool for reaming frustoconical undercuts in cylindrical holes in flint and chert concrete using diamond impregnated blades disposed on the leading edge of expandable cutter elements in such fashion as to maximize the surface area of the cutter blade being used. In addition, cooling and flushing fluid is provided to the undercutting end of the tool to prevent deterioration of the blade and flush away particles of the material being cut.
2. General Background
Various apparatus are known which attempt to ream frustoconical undercuts in the walls of cylindrical holes drilled in concrete. The purpose of undercutting the holes is to provide a frustoconical opening within a cylindrical hole for placement of an expansible anchor bolt. This structure is particularly useful in setting bolts in an existing concrete, stone or other masonary structure where the hole is drilled after the structure is built, as distinguished from a wall having bolts embedded therein before the concrete sets. The undercutting of the hole greatly increases the reliability of the anchor bolt, as compared with an anchor bolt set into a hole having only cylindrical walls and relying on friction to prevent withdrawal of the bolt after it has been expanded. The superior reliability of the anchor bolt accounts for its extensive use in such "fail safe" structures as nuclear reactor containment facilities.
A very early attempt to provide a reamer having sufficient stability and accuracy to adequately undercut the walls of a hole is disclosed in U.S. Pat. No. 1,710,580 issued to LeBus. The reamer comprised a tubular body having an internal sleeve which advanced downwardly against an upwardly curving cutter blade to force the blades downwardly into a horizontal cutting position.
U.S. Pat. No. 1,824,238 issued to Scott for an oil sand bit having a slotted body with a stem sliding therein, the stem being adapted for attachment to a drill pipe. Two blades were pivotally mounted in the slotted body, and the cutting edges of the blades were forced outwardly into a flared cutting position by a downward movement of the stem into the body. Another attribute of this invention was the inclusion of a hollow stem for attaching a water source to the tool and conveying a water supply to the pivotally mounted blades for flushing and cooling purposes.
U.S. Pat. No. 2,060,352 issued to Stokes and discloses a hollow, expansible drill having a plunger located adjacent a pair of pivotally mounted cutter blades. Introduction of fluid into the hollow tool caused the plunger to move downwardly on the slanted upper portions of the pivotally mounted cutter blades, thereby hydraulically extending the cutter blades to their horizontal operating position. Cessation of introduction of the fluid would result in the retraction of the blades into the body of the tool.
U.S. Pat. No. 2,216,895, issued to Stokes, also disclosed a rotary underreamer having a pair of pivotally mounted cutter blades which were extended to their horizontal, operating position by the introduction of a fluid under pressure into the hollow cutting tool.
U.S. Pat. No. 2,872,160 issued to Barg for an hydraulic expansible rotary well drilling bit capable of discharging drilling fluid at the bottom of the bit to ensure upward flushing and removal of the cuttings to the top of a well bore. The expansible drill bit cutters were expanded outwardly by hydraulic pressure which urged a plunger device downwardly against the force of a spring, thereby actuating a rack and pinion device to swing a pair of pivotally mounted blades from a vertical, inoperative position to a flared, horizontal operating position.
U.S. Pat. No. 2,997,119 issued to Goodwin for a drill bit assembly having separately mounted pivotal cutter blades with U-shaped flanges for receiving a plunger head. When the plunger head was advanced into the hole being cut, the separately mounted cutter blades were tilted outwardly into a horizontal position for underreaming purposes.
More recently U.S. Pat. No. 4,091,882 issued to Hashimoto for a drilling tool for use in embedding an anchor bolt with synthetic resin adhesive in a concrete bed.
An expansible drill bit for underreaming a hole while providing circulation of drilling fluids at all times during the underreaming process and afterwards, is the subject of U.S. Pat. No. 3,365,010 issued to Howell et al.
The flaws with the tools in the prior art are most dramatically illustrated in U.S. Pat. No. 4,307,636 issued to Lacey. U.S. Pat. No. 4,307,636 discloses structure for a drilling tool similar to the tool of the present invention, but without providing a means for introducing cooling and circulating fluid into the vicinity of the blades. The forward advance of the interal ram into the surrounding sheath was stopped at a predetermined point only by pin 34, and this pin was subject to breakage and subsequent flaring of the cutting blades to a greater than desired diameter. In addition, the Lacey patent failed to disclose the proper geometric relationship at which to place cutting blades on the cutters to achieve accurate undercutting in concrete having a significant flint and chert content.